Your post - as I understood it, was to change the style i.e. fonts, size, colour etc.
TOC may be basic to any book, but the final outcome is dependant upon which application you use and what it's capabilities are...and those are the only parameters you have to work within. Adobe InDesign is the favoured tool of Tool of many self publishers and it is a costly application and it's TOC or index is perhaps more flexible..but....
If you use iBooks Author, you work with the software as provided.
Apple provide a free application to create what is basically an hybrid - part app and part ePub which formats and creates only what Apple think is appropriate.
You cannot expect iBA to analyse your Pages content and reformat into iBA.
If the individual chapters you Imported from Pages, did not have sections ..then iBA as no reference point and cannot create sections for you, do it has noting to show in the TOC. In iBA individual pages are not shown in the TOC,they are seen at the bottom as "thumbnails".
While Apple created the import for Words and Pages, they do not carry over the format of iBA.
To be frank, most of the time this function is not worth using. Although time consuming, it is, in the long run, better to copy and paste text and create your own Chapters and sections, which will show in the TOC.
Figures seem more a bookmark option....
If you want to send your requirements as feedback. There is a feedback link in the help files.